Integrated optical waveguides, direct-bonded waveguide interface joints, optical routing and interconnects

ABSTRACT

Integrated optical waveguides, direct-bonded waveguide interface joints, optical routing and interconnects are provided. An example optical interconnect joins first and second optical conduits. A first direct oxide bond at room temperature joins outer claddings of the two optical conduits and a second direct bond joins the inner light-transmitting cores of the two conduits at an annealing temperature. The two low-temperature bonds allow photonics to coexist in an integrated circuit or microelectronics package without conventional high-temperatures detrimental to microelectronics. Direct-bonded square, rectangular, polygonal, and noncircular optical interfaces provide better matching with rectangular waveguides and better performance. Direct oxide-bonding processes can be applied to create running waveguides, photonic wires, and optical routing in an integrated circuit package or in chip-to-chip optical communications without need for conventional optical couplers. An example wafer-level process fabricates running waveguides, optical routing, and direct-bonded optical interconnects for silicon photonics and optoelectronics packages when two wafers are joined.

RELATED APPLICATIONS

The patent application is a divisional of U.S. patent application Ser.No. 16/247,262 to Huang et al., filed Jan. 14, 2019, entitled,“Integrated optical waveguides, direct-bonded waveguide Interfacejoints, optical routing and Interconnects,” which claims the benefit ofpriority to U.S. Provisional Patent Application No. 62/635,314 to Huanget al., filed Feb. 26, 2018, entitled, “Integrated optical waveguides,direct-bonded waveguide Interface joints, optical routing andInterconnects,” the entire contents of each of which are herebyincorporated herein by reference.

BACKGROUND

In the past, conventional fabrication of silicon and silicon dioxide(silica) optical waveguides traditionally relied on high temperaturesthat exceeded 1000° C. Such high temperatures damaged or weakenedmicroelectronic devices. Conventional waveguides based on silicon andsilicon dioxide also required a light-bending radius that was too largeto include such optoelectronic circuits on small electronic dies andchips. Ongoing efforts aim to fully integrate silicon photonics withconventional microelectronics in unified packages, where opticalinterconnects provide faster data transfer between dies and microchips,and also faster data transfer within the dies and chips themselves.

Silicon, as a good conductor of infrared light, has become important tooptoelectronics and provides many technical and economic advantages.Silicon photonics can combine the advantages of photonics with thewidespread use of silicon in conventional CMOS manufacturing. Photonicsoffers high-performance communication, low power of operation, and smallsize and weight. CMOS offers volume production, low cost,miniaturization, and high integration. Silicon photonics thereforeprovides high integration, miniaturization, higher bandwidth, lowercost, and lower power of operation. Micro-optoelectronic integrationusing silicon photonics also cuts the cost of optical links.

Compound semiconductors for optoelectronics and silicon photonicscombine an element from group III of the periodic table (e.g., In, Ga,Al) with an element from group V of the periodic table (e.g., As, P, Sb,N). This yields twelve different III-V compounds, but the mostcommercially useful of these are currently GaAs, InP, GaN, and GaP. On asilicon substrate it is very difficult to epitaxially grow quality III-Vsemiconductor materials needed for mass-produced construction ofphotonic devices. Fabrication procedures such as etching are completelydifferent from silicon processes. Moreover, contamination from III-Vsemiconductors must be completely prevented from contact or inclusionwith the silicon of silicon electronics. Thus, it is difficult tointroduce III-V semiconductor compounds into silicon electronics.Polymer waveguides of organic compounds cause less damage to electronicdevices, but they are limited to the uppermost layers available onlyafter electronic circuits have been completed, or to other locationsisolated from the electronic devices being fabricated because theycannot withstand the high temperatures present in electronic devicefabrication.

Silicon photonic circuits most often operate in the infrared at awavelength of 1550 nanometers, at which silicon becomes a good conduitfor transmission of the infrared optical beams. A top and bottomcladding of silicon dioxide (silica) on a waveguide structure made ofsilicon confines the infrared light within the silicon due todifferences in the refraction indices of silicon and silicon dioxide,similar in some respects to how light is conducted in a fiber opticfilament. Silicon photonic devices that use such silicon waveguides canbe constructed by semiconductor fabrication techniques previously usedexclusively for microelectronics. Since silicon is already used as thesubstrate in most conventional integrated circuits for microelectronics,hybrid devices in which the optical and electronic components areintegrated onto a single microchip can be made with conventionalsemiconductor fabrication processes, sometimes even without retooling.

Processes that fabricate photonic devices using silicon and silicondioxide can also utilize conventional silicon on insulator (SOI)techniques that are already well-known in microelectronics, providing aSOI waveguide layer on a wafer, to which optical dies such as LEDs,lasers, and photodetectors may be conventionally attached byless-than-ideal means.

SUMMARY

Integrated optical waveguides, direct-bonded waveguide interface joints,optical routing and interconnects are provided. An example opticalinterconnect joins first and second optical conduits. A first directoxide bond at room temperature joins outer claddings of the two opticalconduits and a second direct bond joins the inner light-transmittingcores of the two conduits at an annealing temperature. The twolow-temperature bonds allow photonics to coexist in an integratedcircuit or microelectronics package without conventionalhigh-temperature photonics processes destroying the microelectronics.Direct-bonded square, rectangular, polygonal, and noncircular opticalinterfaces provide better matching with rectangular waveguides andbetter performance. Direct oxide-bonding processes can be applied tocreate running waveguides, photonic wires, and optical routing in anintegrated circuit package or in chip-to-chip optical communicationswithout need for conventional optical couplers. An example wafer-levelprocess fabricates running waveguides, optical routing, anddirect-bonded optical interconnects for a siliconphotonics-microelectronics package when two wafers are joined.

This summary is not intended to identify key or essential features ofthe claimed subject matter, nor is it intended to be used as an aid inlimiting the scope of the claimed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

Certain embodiments of the disclosure will hereafter be described withreference to the accompanying drawings, wherein like reference numeralsdenote like elements. It should be understood, however, that theaccompanying figures illustrate the various implementations describedherein and are not meant to limit the scope of various technologiesdescribed herein.

FIG. 1 is a diagram of an example optoelectronics package withcomponents coupled by an optically-enabled interposer with direct-bondedwaveguide interface joints.

FIG. 2 is a diagram of an example optical interface between exampleoptical conduits.

FIG. 3 is a diagram of an example optical interface with noncircularcross-section, between example optical conduits.

FIG. 4 is a diagram of example optical waveguides and optical traceswith waveguide interface joints created by processes that include directbonding at low-temperatures.

FIG. 5 is a diagram of an example substrate, such as a silicon oninsulator (SOI) substrate, with photonic waveguides as optical tracesattached to the substrate via direct bonding techniques.

FIG. 6 is a diagram of an example integrated optical waveguidefabricated by a wafer-level process.

FIG. 7 is a diagram of example mode profiles of a silicon ribbedwaveguide with dimensions suitable for optical routing and chip-to-chipcommunications via integrated optical waveguides and direct-bondedwaveguide interface joints.

FIG. 8 is a flow diagram of an example method of making an integratedoptical waveguide in a wafer-level process

DESCRIPTION Overview

This disclosure describes integrated optical waveguides, direct-bondedwaveguide interface joints, optical routing and interconnects. Exampleprocesses and apparatuses described herein provide various ways of usingdirect bonding techniques to create integrated optical waveguides,direct-bonded waveguide interface joints, photonic wire, andchip-to-chip optical routing. Optical transmission and routing terms andphrases, such as “optical conduit,” “optical trace,” “waveguide,”“photonic wire,” “optical circuit,” and component parts of these, may beused somewhat interchangeably herein, depending on context.

An example optical interconnect joins first and second optical conduits.A first direct oxide bond performed at room temperature joins outercladdings of the two optical conduits, and a second direct bond joinsthe inner light-transmitting cores of the two conduits at an annealingtemperature, for example. The second direct bonding of the inner coresis formed during an annealing process due to the differential incoefficients of thermal expansion between the outer cladding and theinner core of each optical conduit being joined. These twolow-temperature bonds allow photonics processes to be applied in asingle integrated circuit or microelectronics package withoutconventional high-temperature photonics processes destroying themicroelectronics. Direct-bonded square, rectangular, polygonal, andnoncircular optical interfaces with no gaps or minimal gaps in theinterface between surfaces, and no detrimental extra layers added tomake the interface, provide better matching with rectangular waveguidesand provide better performance. Direct oxide-bonding processes can beapplied to create running waveguides, photonic wires, and opticalrouting in an integrated circuit package or in chip-to-chip opticalcommunications without need for conventional optical couplers. Anexample wafer-level process fabricates running waveguides, opticalrouting, and direct-bonded optical interconnects for a siliconphotonics-microelectronics package when two wafers are joined.

The example integrated optical waveguides, direct-bonded waveguideinterface joints, optical routing and interconnects described hereinprovide nano-small geometrical structures for compatibility with siliconelectronics, so that very small optoelectronics packages may beproduced.

The example integrated waveguides described herein can accommodatepassive and dynamic photonic devices, wavelength filters, modulators, aswell as compatibility with light emission functions, and light detectionfunctions with low propagation loss.

The example optical waveguides used as photonic routing can havenano-small core dimensions and micrometer-scale bending sections tomatch the scale of microelectronic circuits. The example waveguides canbe constructed on silicon-on-insulator (SOI) substrates, where theuppermost silicon layer of the SOI substrate is employed as thewaveguide core, eliminating the need to specially form the corematerial. The cladding material can be silica-based compounds likesilicon dioxide, formed by low-temperature processes, plasma-enhancedchemical vapor deposition, and so forth. Bonding between materials atthe example optical interfaces can be performed by low-temperature DBIor ZIBOND direct bonding processes (Xperi Corporation, San Jose,Calif.). These features result in optoelectronic packages that have lowpower consumption and low packaging cost.

Example Systems

FIG. 1 shows an example optoelectronics package 100, with anoptoelectronic computing chip 102 optically coupled with anoptoelectronic memory stack 104 through an optically-enabled interposer106. The interposer 106 may be a substrate or part of a substrate, ormay be an optoelectronic chip in its own right.

The interposer 106 has one or more optical conduits 108 built into theinterposer 106. In an implementation, the optical conduits 108 mayinclude a waveguide or a photonic wire. In a silicon photonicsimplementation, a ribbed and/or rectangular waveguide version of theoptical conduits 108 may transmit or guide (“conduct”) infrared light asoptical communications power.

The optical conduits 108 each generally include an inner core 110surrounded by an outer cladding 112. The inner core 110 transmitsoptical power in one of several possible modes, while the outer cladding112 confines the infrared light within the silicon inner core 110 due todifferences in the refraction indices of silicon and silicon dioxide. Ina rectangular waveguide implementation of the optical conduits 108, topand bottom claddings 112 of silicon dioxide on a silicon waveguidestructure of rectangular cross-section confine the infrared light withinthe silicon. In a ribbed implementation of the silicon waveguide opticalconduits 108, a rectangular rib on one side of the rectangular waveguidestructure guides, directs, and/or bends the optical power wavefront.Example optical interfaces 114 optically join device optical conduits116 & 118 of the optoelectronic computing chip 102 and of theoptoelectronic memory stack 104 with the optical conduits 108 of theinterposer 106, in this example.

FIG. 2 shows an example optical interface 114 between example opticalconduit 116 and optical conduit 108. The optical interface 114 may alsoinclude electrical contacts bonded to each other with low-temperaturedirect bonds (not shown). The example optical interface 114 provides adirect bonding waveguide interface joint. A first example techniqueapplies direct oxide bonding to create the optical interface 114 betweena first optical component, such as the photonics of the optoelectroniccomputing chip 102 and a second optical component, such as an opticalwaveguide version of the optical conduits 108 of the interposer 106. Theexample technique for making optical interfaces can be used in theconstruction of 3D and 2.5D photonic integrated circuits, for example.

In the example process for creating an optical interface 114, an innercore 110 of the optical conduits 116 & 108 may be made of a firstmaterial that conducts light at one or more wavelengths. The innerlight-transmitting material may be silicon (Si), or other opticalmaterials such as Zr0₂, HfO₂, TiO₂, LiNbO₃, Nb₂O₅, SrTiO₃, or ZnS, forexample. The outer cladding 112 of the optical conduits 116 & 108 has alower refractive index than the material that makes up the inner core110 of the optical conduits 116 & 108, so that the inner core 110transmits the light and the outer cladding 112 reflects or refractslight that is leaving the inner core 110 back into the inner core 110.The outer cladding material may be silicon dioxide (SiO₂) in the case ofa silicon inner core 110, for example, or may be a polymer, such aspolyimide, parylene, or other material with a suitable refractive indexwith respect to the material of the inner core 110 of the opticalconduits 116 & 108.

In an implementation, through a direct bonding process, such as a directoxide bonding process or an oxide-to-oxide direct bonding process, theouter cladding 112 is joined to a counterpart of the same material onthe other side of the interface 114. In an implementation, the exampledirect oxide-bonding process takes place at room temperature, withminimal or no gaps, between surfaces being joined, and no detrimentalextra layers created or introduced into the optical interface 114 duringthe process.

Depending on materials and process, there may be an allowable gap 200 ormultiple partial gaps between the inner cores 110, at the surfaces beingjoined, or there may be no gaps. A permissible gap 200 has a gap size(vertical gap) less than one-quarter of the wavelength of theoperational optical signal being conducted as electromagnetic waves. Thegap 200 is shown as exaggerated in FIG. 2, for purposes of illustration.For silicon photonics, using silicon as the inner core 110 of a conduit108, the signal is often conducted by infrared light at a wavelength ofapproximately 1550 nanometers, or in the range of approximately1100-1550 nanometers. So in some circumstances, a gap 200 of less thanapproximately 387.5 nanometers is permissible in the interface betweenconduits 108 & 116, either as part of a fabrication process or adefects. The inner cores 110 of the optical conduits 116 & 108, withinthe respective outer claddings 112, are also direct-bonded in a secondstep to their counterparts of inner core material on the other side ofthe interface 114, during an annealing step or separate annealingprocess, for example. The annealing process may have an annealingtemperature that is at least slightly higher than room temperature, butis still a very low-temperature when compared with conventionalfabrication temperatures for conventional optical waveguides. Thedirect-bonding of the inner cores 110 to each other to complete theoptical interface 114 also introduces minimal or no gaps and nodetrimental extra layers of material into the interface 114 beingformed, during the process.

The first direct oxide bond and the second direct bond join the firstoptical conduit 116 and the second optical conduit 108 together in alayerless join or a join with no detrimental intervening layers betweenthe first optical conduit 116 and the second optical conduit 108.Likewise, the first direct oxide bond and the second direct bond jointhe first optical conduit 116 and the second optical conduit 108together in a join with no gap or permissible gap between the firstoptical conduit 116 and the second optical conduit 108.

The optical interface 114 may also include electrical contactsassociated with each of the first optical conduit 116 and the secondoptical conduit 108, wherein a first set of electrical contacts of thefirst optical conduit 116 are direct oxide bonded or direct bonded to asecond set of electrical contacts of the second optical conduit at theoptical interface 114.

In an implementation, an example apparatus includes a first opticalconduit 116 on a first side of an optical interface 114 of a photonicdevice, a second optical conduit 108 on a second side of the opticalinterface 114 of the photonic device, and a first direct oxide bondbetween outer claddings 112 of the first optical conduit 116 and thesecond optical conduit 108. There is a second direct bond between innercores 110 of the first optical conduit 116 and the second opticalconduit 108. The apparatus may further include a first optical component102 on the first side of the optical interface 114, the first opticalcomponent 102 having at least a first planar surface exposing across-section of the first optical conduit 116, and a second opticalcomponent 104 on the second side of the optical interface 114. Thesecond optical component 104 also has at least a second planar surfaceexposing a cross-section of the second optical conduit 108, which may bean optical waveguide. The second optical conduit 108 also has an innercore 110 and an outer cladding 112 around the inner core 110.

The first direct oxide bond between the outer claddings 112 of the twooptical conduits 116 & 108 can be an oxide bond formed at roomtemperature, such as a ZIBOND brand of direct oxide-to-oxide bonding(Xperi Corporation, San Jose, Calif.). The second direct bond of theinner cores 110 can be a metal-to-metal, semiconductor-to-semiconductor,or photonic-material-to-photonic-material bond formed at an annealingtemperature used for strengthening, curing or setting the previousdirect oxide bond for the outer claddings 112. For example, two surfacesof silicon may form crystal lattice bonds at the optical interface witheach other. ZIBOND bonding is a low-temperature wafer-to-wafer ordie-to-wafer bonding technique between wafers or dies with the same ordifferent coefficients of thermal expansion (CTE), using alow-temperature homogeneous (oxide-to-oxide) direct bonding technology.ZIBOND bonding offers multiple benefits over conventional bondingtechniques such as adhesives, anodic bonding, eutectic bonding and glassfrit. Bonding is performed at room temperature, which enhances overallyield and reliability, by eliminating the negative effects associatedwith coefficient of expansion (CTE) mismatch, warpage and distortion.Higher throughput and lower cost-of-ownership are realized by usingindustry-standard wafer alignment and bonding equipment. Withoutrequiring elevated temperature or high pressure during bonding, thehigh-throughput of the ZIBOND bonding fabrication process minimizescost-of-manufacturing during mass-production for high volume marketapplications. During ZIBOND processing, industry standard dielectricsurfaces like silicon dioxide or silicon carbide nitride are polished tolow surface roughness using conventional chemical-mechanical polishing(CMP) tools, and nitrogen-based chemistries are applied throughconventional plasma etch processing. Prepared wafer surfaces are thensimply aligned and placed together, resulting in the spontaneousformation of chemical bonds between die and/or wafers. A very strong,low distortion chemical bond with a bond strength about half thestrength of silicon can be obtained at room temperature, and a reliablehermetic bond stronger than silicon can be obtained after moderateheating to about 150° C. in batch processes outside of the alignment andplacement tool, for example.

FIG. 3 shows an example optical interface 114 between the first opticalconduit 116 and the second optical conduit 108, with a noncircularcross-section 402 in a plane of the optical interface 114. The opticalinterface 114 may also include electrical contacts bonded to each otherwith low-temperature direct bonds (not shown). The example opticalinterface 114 provides a direct bonding waveguide interface joint. In animplementation, the optical interface 114 comprises a join having anoncircular cross-section between the first outer cladding 112 of thefirst optical conduit and the second outer cladding 112 of the secondoptical conduit in the plane of the optical interface. The opticalinterface 114 also has a noncircular join between the first inner core110 of the first optical conduit and the second inner core 110 of thesecond optical conduit.

In one instance, the optical interface 114 may have a rectangularcross-section, a square cross-section, or a polygonal cross-section in aplane of the optical interface 114. In some cases, the first opticalconduit 108 on one side of the optical interface 114 has a noncircular,rectangular, square, or polygonal cross-section and the other opticalconduit 116 has a circular cross-section in the plane of the opticalinterface.

FIG. 4 shows example optical waveguides 400 created by processes thatinclude direct bonding at low-temperatures. The optical waveguides 400,including ribbed waveguides 402, can be routed as optical traces 404 orphotonic wires in microelectronic and optoelectronic circuit layouts.The low-temperature direct bonding technique can also be used to attachthe optical waveguides 400 to chips 102 & 406 and to other componentswith example optical interfaces 114 in ways that can eliminate the needfor optical couplers in chip-to-chip communications. The example opticalinterface 114 provides a direct bonding waveguide interface jointbetween the optical traces 404 and the optoelectronic microchip 406. Thewaveguides 400, fabricated using low-temperature bonding techniques, canbe formed as optical traces 404 along the surface layers of chips 406,and between chips, to provide optical routing similar to the routing ofelectrical conductors, at reduced size over conventional opticalchannels.

An example optoelectronic apparatus includes an optical trace 404 bondedto a die or a chip 406 made at least in part of a semiconductormaterial, and a direct oxide bond between the optical trace 404 and thedie or chip 406. The direct oxide bond may be an oxide-to-oxide bondformed at room temperature or at a temperature near or below roomtemperature. Material used for the waveguides 400 employed at opticaltraces 404 are optically transparent or photonic materials, includingsome semiconductors. The direct oxide bond itself can be opticallytransparent, or optically transparent at least in part.

In one layout, the optical trace 404 transmits a light orelectromagnetic radiation between a first die or chip 102 and a seconddie, chip 104, or stack of dies. The optical trace 404 may be directlyoxide-bonded to a first die or chip 102 and to a second die or chip 104.The optical trace 404 can provide an optical path between the first dieor chip 102 and the second die 104 or chip without conventional inlineoptical couplers.

In an implementation, on a given die or microchip 406, the optical trace404 may be a rib member 408 of an optical waveguide. The rib member 408is direct bonded 410 to a semiconductor material of the die or microchip406 to make the optical waveguide 402 serving as an optical trace 404,wherein the optical waveguide 402 comprises the rib member 408, thedirect bond 410, and the semiconductor material of the die or themicrochip 406.

FIG. 5 shows a substrate, such as a silicon on insulator (SOI) substrate500, with photonic waveguides as optical traces 404 attached to thesubstrate 500 via direct bonding techniques. The optical traces 404 arerouted on the substrate 500 to and between microchips 502 & 504 & 506.The optical traces 404 may be rectangular waveguides 400 or ribbedwaveguides 402. In an implementation, only the rib member 408 isdirect-bonded to a semiconductor material of the substrate 500, such asa silicon on insulator (SOI) substrate 500, to create waveguides 400 &402 for routing optical paths. The tops of waveguides 400 and 402 may beclad with an oxide 112 of suitable refractive index, such as silicondioxide, to complete the waveguide structures. The waveguides 400 & 402may also be attached as a layer of semiconductor, for example, to an SOIwafer or substrate, and then etched into waveguide structures 400 & 402and topped with silicon dioxide or other material with suitable index ofrefraction to make optical waveguide structures 400 and 402. The opticaltraces 404 as completed waveguides can provide a continuous opticaltrace 404, an optical bus, and an unbroken optical pathway between themultiple dies or microchips 502 & 504 & 506 across the substrate 500,using low-temperature direct bonding techniques.

The low-temperature direct bonding techniques are used to attach theoptical traces 404 to chips 502 & 504 & 506 and to other optoelectroniccomponents with example optical interfaces 114 that eliminate the needfor optical couplers in chip-to-chip communications. The example opticalinterfaces 114 provides direct bonding waveguide interface jointsbetween the optical traces 404 and optoelectronic microchips 502 & 504 &506.

FIG. 6 shows an example photonic or optoelectronic apparatus, such as anintegrated optical waveguide 600, fabricated by wafer-level fabrication.The wafers for making the optoelectronic apparatus may have dies foroptoelectronics or microelectronics, and may also have optical deviceswith III-V semiconductor optical compounds, mounted to one or more ofthe wafers.

To make the example apparatus or integrated optical waveguide 600, anexample process includes coupling optical components and electricalcontacts together across an optical interface at a single bondingsurface between the wafers, while simultaneously fabricating photonicwaveguides for optical routing in the optoelectronic package orstructure being formed. The use of low-temperature direct oxide bonds inthis example process allows unification or convergence of siliconphotonics and microelectronics together in the same wafer-producedpackage. Some aspects of the example process can also be used to formwaveguides in die-to-die processes or to perform vertical direct opticalcoupling and electrical coupling of contacts from one die to anotherwith minimal or no gaps and no detrimental extra layers, and withoutrequiring underfill or bumps.

In one implementation, a channel 602 is etched in a first wafer 604 ofsilicon to make a silicon pillar 606 surrounded by the channel 602 inthe first wafer 604. The channel 602 may be filled with a dielectricthat has a suitable refractive index relative to the silicon to createan optical conduit and part of a waveguide.

A recess 608 is formed in the first wafer 604 of silicon in an areaaround the channel 602 and silicon pillar 606. A first oxide material isdeposited in the recess 608 for later purposes of direct oxide-bondingbetween wafers, at low-temperature.

On a second wafer 610 made of silicon, a trench 612 is etched, having anangled side 614, such as at least one 45 degree side in the trench 612.A second oxide is deposited in the trench 612. The oxide deposited inthe trench 612 of the second wafer 610 may be the same oxide asdeposited in the recess 608 of the first wafer 604.

The trench-side of the second wafer 610 is bonded to at least an oxidelayer 616 of a third wafer 618 to make an interposer 620. The interposer620 may be thinned at this point, as desired. The first wafer 604 isthen bonded to the interposer 620 by direct oxide-to-oxide-bonding ofthe first oxide in the recess 608 of the first wafer 604 to at least theoxide in the trench 614 of the second wafer 610 to make the exampleintegrated waveguide 600 of silicon, or other optical apparatuses bondedat a single waveguide interface plane with direct oxide bonding.

Prior to bonding the first wafer 604 to the interposer 620 to make theintegrated waveguide 600, the silicon pillar 606 of the optical conduitof the first wafer 604 is aligned with the angled side 614 of the trench612 of the interposer 620 in order to fabricate an optical pathway 622that connects optical power between a component 624 mounted on the firstwafer 604 and the integrated waveguide 600. In an implementation, theintegrated waveguide 600 guides the optical power around a corner formedby the angled side 614 of the trench 612 of the interposer 620, that is,from a vertical silicon pillar 606, for example, to a horizontal layer626 of the silicon.

In an implementation, aligning the silicon pillar 606 with a 45 degreeside 614 of the trench 612 prior to the bonding makes an integratedwaveguide 600 capable of guiding infrared light propagating verticallyfrom the silicon pillar 606 through a 90 degree change in direction intothe horizontally disposed silicon layer 626 in the interposer 620.

The example process may use direct oxide-to-oxide-bonding between theoxide in the recess 608 of the first wafer 604 and the oxide in thetrench 612 of the second wafer 610 or interposer 620, with the bondingat room temperature, which favors microelectronics located in the samevicinity, as higher temperatures can be detrimental to themicroelectronics. The low bonding temperature also allows optoelectroniccomponents with III-V semiconductor compounds to be fully finished andmounted prior to the bonding. Conventionally, components with III-Vsemiconductor compounds need special handling because they cannotwithstand conventional microelectronics bonding temperatures.

The silicon of the pillar 606 and the silicon in the top horizontallayer 626 of the interposer 620 are joined together at the same time asthe oxide interface, with spontaneous crystal lattice bonding at anannealing temperature slightly higher than room temperature.

FIG. 7 shows diagrams of direct oxide-to-oxide bond-enabled siliconribbed waveguides and example mode profiles. At dimensions of W=1.4 μm,H=1.5 μm, and r=0.39 at 1.55 μm, an example polarization-independent SOIribbed waveguide has a fundamental transverse electric-like (TE-like)mode 702 (Ex field profile) with no electric field in the direction ofpropagation, and the example polarization-independent SOI ribbedwaveguide has a fundamental transverse magnetic-like (TM-like) mode 704(intensity profile) with no magnetic field in the direction ofpropagation.

FIG. 8 shows an example method of making an integrated optical waveguidein a wafer-level process. Operations of the example method are shown inindividual blocks.

At block 802, a channel is etched in a first wafer of silicon to make asilicon pillar surrounded by the channel in the first wafer. The methodis not limited to silicon, but can be implemented in silicon as anexample, to combine optical communications with microelectronics in asilicon photonics package.

At block 804, the channel may be filled with a dielectric or othermaterial of suitable refractive index. The dielectric and the pillarbeing surrounded by the dielectric comprise an optical conduit forinfrared light, in the case of silicon.

At block 806, the silicon on one side of the first wafer is etched orotherwise removed to form a recess around the optical conduit on thatside of the first wafer.

At block 808, a first oxide is deposited in the recess.

At block 810, a trench is etched on a second wafer made of silicon, thetrench having an angled side, such as at least one 45 degree side.

At block 812, a second oxide is deposited in the trench of the secondwafer. The second oxide may be the same oxide compound as deposited inthe recess of the first wafer, at block 808, or may be a differentoxide.

At block 814, a trench side of the second wafer is bonded to an oxidelayer of a third silicon wafer, such as a silicon on insulator (SOI)wafer, to make an interposer.

At block 816, the first wafer with the optical conduit is bonded to theinterposer after alignment to make an integrated waveguide of silicon,including direct oxide-to-oxide-bonding of the first oxide in the recessof the first wafer to at least the second oxide in the trench of thesecond wafer.

In the specification and following claims: the terms “connect,”“connection,” “connected,” “in connection with,” and “connecting,” areused to mean “in direct connection with” or “in connection with via oneor more elements.” The terms “couple,” “coupling,” “coupled,” “coupledtogether,” and “coupled with,” are used to mean “directly coupledtogether” or “coupled together via one or more elements.”

While the present disclosure has been disclosed with respect to alimited number of embodiments, those skilled in the art, having thebenefit of this disclosure, will appreciate numerous modifications andvariations possible given the description. It is intended that theappended claims cover such modifications and variations as fall withinthe true spirit and scope of the disclosure.

1. An apparatus, comprising: an optical trace bonded to a die or a chip,the die or the chip made at least in part of a semiconductor material;and a direct oxide bond between the optical trace and the die or thechip.
 2. The apparatus of claim 1, wherein the direct oxide bondcomprises an oxide-to-oxide bond formed at room temperature or at atemperature near or below room temperature.
 3. The apparatus of claim 1,wherein the optical trace comprises one of an optically transparentmaterial, a photonic material, or a semiconductor material, and thedirect oxide bond is optically transparent, at least in part.
 4. Theapparatus of claim 1, wherein the optical trace transmits a light or anelectromagnetic radiation between a first die or chip and a second dieor chip.
 5. The apparatus of claim 4, wherein the optical trace isdirect oxide bonded to the first die or chip and to the second die orchip.
 6. The apparatus of claim 4, wherein the optical trace provides anoptical path between the first die or chip and the second die or chip inthe absence of an optical coupler.
 7. The apparatus of claim 1, whereinthe optical trace comprises a rib member of an optical waveguide, therib member direct oxide-bonded to a semiconductor material of a die or achip to make the optical waveguide, wherein the optical waveguidecomprises the rib member, the direct oxide bond, and the semiconductormaterial of the die or the chip.
 8. The apparatus of claim 1, whereinthe optical trace comprises a rib member of an optical waveguide, therib member direct oxide-bonded to a substrate; wherein the substrate isat least partly optically transparent; and wherein the optical waveguidecomprises the rib member, the direct oxide bond, and the at least partlyoptically transparent substrate.
 9. The apparatus of claim 1, whereinthe optical trace is direct oxide-bonded to a substrate and to multipledies or chips; and wherein the optical trace provides a continuouswaveguide, an optical bus, and an unbroken optical pathway between themultiple dies or chips.
 10. The apparatus of claim 1, wherein theoptical trace bonded to the chip, and the chip comprises anoptoelectronic chip comprising an optical conduit.
 11. The apparatus ofclaim 10, wherein a composition of a inner core of the optical conduitis selected from the group consisting of Si, ZrO₂, HfO₂, TiO₂, LiNbO₃,Nb₂O₅, SrTiO₃, and ZnS.
 12. The apparatus of claim 1, further comprisinga second optical trace bonded to the die or the chip.
 13. The apparatusof claim 1, wherein the optical trace is formed in an optically-enabledinterposer.
 14. The apparatus of claim 1, wherein the optical tracecomprises a rectangular waveguide.